The aatma has been in Sumati's body for about a few days now. Scientifically, that is not possible. An aatma cannot possess a human body for more than a few moments, otherwise it can seriously injure the host body.
Eventually, the spirit of the body begins to fight back and resist pushing the aatma back out because it doesn't belong. The way the show is having this aatma in Sumati's body for long periods of time makes no sense because being in a human body takes a lot of energy out of an aatma. Plus, when the real Sumati comes back she will be completely lost.
Just my two cents.
xo,
Miss Independent